Synthesis of phosphonated graphene oxide by electrochemical exfoliation to enhance the performance and durability of high-temperature proton exchange membrane fuel cells

The doping of functionalized graphene oxide(GO)in the membranes becomes a promising method for improving the performance of high-temperature proton exchange membrane fuel cells(HT-PEMFC).Phosphonated graphene oxide(PGO)with a P/O ratio of 8.5%was quickly synthesised by one-step electrochemical exfoliation based on a three-dimensiaonal(3D)printed reactor and natural graphite flakes.Compared with the GO prepared by the two-step electrochemical exfoliation method,the PGO synthesized by the one-step electrochemical exfoliation can better improve the performance of the membrane-electrode-assembly(MEA)based on the polybenzimidazole(PBI)membrane in the HTPEMFC.The doping of 1.5 wt%GO synthesised by electrochemical exfoliation with the 2-step method or reactor method in PBI increased the peak power density by 17.4%or 35.4%compared to MEA based on pure PBI membrane at 150℃,respectively.In addition,the doping of PGO in PBI improves its durability under accelerated stress test(AST).

Electrochemical exfoliation of two-dimensional layered black phosphorus and applications

With the discovery of graphene,black phosphorus(BP)has been rediscovered as a two-dimensional(2 D)layered material.Since its first preparation in 2014,2 D BP has elicited immense interest,and has exhibited excellent properties,such as distinct pleated structures in layers,adjustable direct bandgap,high carrier mobility,moderate on/off ratio,large specific surface area,and various interesting in-layer anisotropies.However,the realization of these excellent properties depends on the preparation of highquality 2 D BP sheets.Electrochemical exfoliation methods are typically performed under mild conditions,thus,these methods are convenient,controllable,and can produce high-quality 2 D BP sheets.This review summarizes research progress in BP sheets preparation through anodic,cathodic,and electrolyte exfoliation in recent years.Different exfoliating methods affect the quality of 2 D BP sheets.Moreover,possible exfoliating mechanisms and the potential applications of different exfoliating methods are summarized and discussed in detail.Lastly,the shortcomings of existing research on electrochemical exfoliation are presented,and suggestions and prospects for future research on the electrochemical exfoliation of 2 D BP are proposed.

Synthesis of graphene materials by electrochemical exfoliation: Recent progress and future potential

Synthesis of structurally controlled graphene materials is critical for realizing their practical applications.The electrochemical exfoliation of graphite has emerged as a simple method to produce graphene materials.This review examines research progress in the last 5 years,from 2015 to 2019.Graphene material synthesis methods generally have a trade‐off between increasing production yield and achieving better material property control.The synthesis conditions for synthesizing pristine graphene,graphene oxide(GO),and graphene composites are significantly different.Thus,in this review,we first discuss synthesis methods for graphene materials with high C/O ratios from four aspects:graphite electrodes,equipment engineering,electrolytes,and additional reduction methods.Next,we survey synthesis methods for GO and examine how the pretreatment of the graphite electrodes,electrolytes,and operation parameters,such as applied voltages,electrolyte temperatures,and mechanical forces,affect the quality of GO.Further,we summarize electrochemical exfoliation methods used to dope graphene materials,introduce covalent functional groups,incorporate various nanoparticles,and assembly of graphene architectures.For all synthesis methods,we compare the properties of resulting graphene materials such as C/O ratios,lateral size,layer numbers,and quality characterized by Raman spectroscopy.Lastly,we propose our perspectives on further research.We hope this review stimulates more studies to realize the on‐demand production of graphene materials with desired properties using electrochemical exfoliation methods.

ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY DURING CORROSION PROCESS OF 8090 Al-Li ALLOY IN EXCO SOLUTION

The corrosion behavior and electrochemical impedance spectroscopy (EIS) features of 8090 Al-Li alloys in EXCO solution were investigated, and the EIS was simulated using an equivalent circuit. At the beginning of immersion in EXCO solution, the EIS is comprised by a depressed capacitive arc at high-mediate frequency and an inductive arc at low frequency, and the inductive component decreases and disappears with im- mersion time. Once exfoliation or severe pitting corrosion is produced, two capacitive arcs appear in the EIS. These two capacitive arcs are originated from the two parts of the corroded alloy surface, the original flat alloy surface and the new inter-face exposed to the aggressive EXCO solution due to the exfoliation or pitting corrosion. Some corrosion development features of 8090 Al-Li alloys in EXCO solution can be obtained through simulated EIS information.

Electrochemically exfoliated Ni-doped MoS_(2) nanosheets for highly efficient hydrogen evolution and Zn-H_(2)O battery

Thanks to tunable physical and chemical properties,two-dimensional(2D)materials have received intensive interest,endowing their excellent electrocatalytic performances for applications in energy conversion.However,their catalytic activities are largely determined by poor adsorption energy and limited active edge sites.Herein,a one-step electrochemical exfoliation strategy was developed to fabricate 2D Ni-doped MoS_(2)nanosheets(Ni-EX-MoS_(2))with a lateral size of500 nm and thickness of3.5 nm.Profiting from high electrical conductivity and abundant exposing active sites,Ni-EX-MoS_(2)catalyst displayed an admirable performance for electrochemical hydrogen evolution reaction(HER)with a low overpotential of 145 m V at 10 m A/cm^(2)as well as a small Tafel slope of 89 m V/dec in alkaline media,which are superior to those of the most reported MoS_(2)-based electrocatalysts.The formed Ni species with tuning electronic structure played a crucial role as primary active center of Ni-EX-MoS_(2),as well as the forming stable 1T/2H phase MoS_(2)interface demonstrated a synergistic effect on electrocatalytic HER performance.Further,Ni-EX-MoS_(2)was employed as a cathode electrode for alkaline Zn-H_(2)O battery,which displayed a high power density of 3.3 m W/cm^(2)with excellent stability.This work will provide a simple and effective guideline for design of electrochemically exfoliated transition metal-doped MoS_(2)nanosheets to inspire their practical applications in energy catalytic and storage.

Synthesis,characterization and life cycle assessment of electrochemically exfoliated KOH-activated holey graphene

Graphene materials have drawn tremendous attention in recent years.The formation of holes and pores on graphene sheets can provide transfer channels and facilitate the ion/electron transport kinetics.In this study,graphene nanosheets were prepared electrochemically,and then,they were used as the starting material for the preparation of holey graphene(HG)through the KOH activation process.The weight ratio of initial electrochemically exfoliated graphene(EEG)to KOH was optimized according to the morphological features,BET surface area examination,graphene number of layers calculated from XRD patterns,and the ID/IG ratio obtained from Raman analysis.Results showed that increasing the KOH amount led to the achievement of higher values of ID/IG and surface area and less re-stacking of graphene sheets which occurs because of the heat treatment process.The environmental burdens of the production routes for the preparation of EEG and HG were investigated by cradle-to-gate life cycle assessment(LCA).The LCA results of EEG production indicated that electricity with the contributions of 94%,91%,82%,and 75%of the total impact in four environmental categories,including fossil fuel depletion,ozone depletion,global warming,and smog was the main environmental weakness.In the pore generation process,KOH was recognized as the biggest contributor(about 51%to 83%of the total impact)in six impact categories,including ozone depletion,non-carcinogenics,smog,global warming,carcinogenics,and eutrophication which could be attributed to its high consumption amount(21.9 kg).This work offers environmental considerations for the development of sustainable graphene materials.

Unlocking the charge doping effect in softly intercalated ultrathin ferromagnetic superlattice

The electrolyte-assisted exfoliation strategy is widely employed to synthesize ultrathin two-dimensional(2D)materials.Yet,spins in 2D magnets are susceptible to the electrolyte due to the underlying charge doping effect.Hence,it is crucial to understand and trace the doping process during the delamination of 2D magnets.Taking the prototype Fe_(3)GeTe_(2),we utilized soft organic cations to exfoliate the bulk and obtain a freestanding organ-ic–inorganic hybrid superlattice with a giant electron doping effect as high as 6.9×10^(14)/cm^(2)(~1.15 electrons per formula unit).A remarkable ferromagnetic transition exceeding 385 K was revealed in these superlattices,together with unique anisotropic saturation magnetization.The doping enhanced the in-plane electron–phonon coupling and thus optimized originally poor indirect double-exchange scenario for spin electrons.The emerging vertical magnetization shift phenomenon served to evaluate the uniformity of charge doping.The above findings provide a new perspective for understanding the role of parasitic charge in 2D magnetism.

A nanosilica/exfoliated graphene composite film-modified electrode for sensitive detection of methyl parathion

Graphene nanosheets （GS） were easily prepared through liquid-phase exfoliation of graphite powder in N,N-dimethylformamide （DMF） with the assistance of sodium citrate. Then, GS was coated onto a glassy carbon electrode （GCE） surface by drop to fabricate a GS]GCE nanointerface. Subsequently, by using tetraethylorthosilicate sol as precursor, nanosilica was electrochemically deposited onto the GS]GCE surface to produce a nanocomposite film electrode （nanosilicaJGSJGCE）. Electrochemical behaviors of methyl parathion （MP） on the nanosilica/GS/GCE surface were investigated thoroughly. It was found that the nanosilicaJGS nanocomposites can improve the redox peak currents of MP significantly due to the synergetic effect. The oxidation peak current was linearly related to MP concentration in the range from 0.0005 μmol/L to 5.6 μmol/L. The detection limit was calculated to be 0.07 nmol/L （SJN = 3）. The developed method was used to determine MP in real samples. The recoveries were in the range from 95.4% to 104.2%, demonstrating satisfactory results.